The flash disk is an internal persistent mass storage device and can be used for any application purpose.
It has a memory capacity of 8 GB (preformatted).
The flash disk is capable of high data throughput, however, the actual values to be achieved depend on the use cases. If the performance seems to get insufficient, check the following:
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If the PLCs CPU load is high, reduce overall CPU load of the PLC to have more performance for file operations.
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If the device has low free space, cleanup the disk.
Please consider the cluster size of 4 kB in your application design to achieve optimal usage of the flash disks space and access performance. For example, 10 files with 10 byte each require 10*4 kB disk space, while 1 file with 100 byte requires only 4 kB.
Number of max. write cycles
Technically, the flash chip used in the flash disk has 20000 erase cycles (Write cycles).
Due to the produced write overhead, the optimum achievable number of write cycles is 10000 (for typical payload sizes of 256 kB).
Example
The write overhead is indicated by the write amplification factor (WAF).
|
Typical payload sizes |
WAF |
Max. write cycles |
|---|---|---|
|
256 kB |
2 |
10000 |
|
128 kB |
4 |
5000 |
|
64 kB |
8 |
2500 |
|
... |
... |
... |
|
1024 Byte |
512 |
< 40 |
|
512 Byte |
1024 |
< 20 |
It is recommended to use the respective function blocks to monitor the status of the flash disk.
Since FW version 3.3.0, there is also a diagnosis event supported when the user flash memory reaches the end of its life cycle.
Lifetime of flash disk will also depend on the operating environment.
E.g. high ambient temperatures will impose stress on the user flash memory and reduce the total overwrites achievable.
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Maximum write speed is 20 MB/s (continuous write of sequential data).
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Read cycles are unlimited.